Muriatic will react violently with zinc and eat it off, additionally, the resulting vapor is also toxic. You would have to spray all the surfaces in the firebox and cook chamber since the area where the heat enters the chamber will also be above a temperature that would release poison gas. The smoker is not usable as built and removing the zinc also can be dangerous to your health. Proceed very carefully at your own risk.

I just realized that. the worst part, I just spent a week having him build it. Is there anyway to salvage it?

Build a fire in it.... That will burn off the zinc..... do that for all that is galvanized......

BE SURE TO STAND UP WIND AND DO NOT BREATHE THE FUMES.... The zinc coating should turn a yellowish color when burnt... clean it out very good.... oil the surfaces and condition the smoker as you would cast iron cookware or woks....